Method and structure for desulfurizing gasoline or diesel fuel for use in a fuel cell power plant

ABSTRACT

A sulfur scrubbing method and structure is operable to remove substantially all of the sulfur present in an undiluted oxygenated hydrocarbon fuel stock supply which can be used to power an internal combustion engine or a fuel cell power plant in a mobile environment, such as an automobile, bus, truck, boat, or the like, or in a stationary environment. The fuel stock can be gasoline, diesel fuel, or other like fuels which contain relatively high levels of organic sulfur compounds such as mercaptans, sulfides, disulfides, thiophenes, and the like. The undiluted hydrocarbon fuel supply is passed through a desulfurizer bed which is provided with a high surface area nickel reactant, and wherein essentially all of the nickel reactant in the scrubber bed reacts with sulfur in the fuel stream, so as to remove sulfur from the fuel stream by converting it to nickel sulfide on the scrubber bed. The desulfurized organic remnants of the fuel stream continue through the remainder of the fuel processing system in the fuel cell power plant, or through the internal combustion engine. The desulfurizer bed is preferably formed from a high surface area ceramic foam monolith, the pores of which are coated with the high surface area nickel reactant. The use of the foam monolith combined with the high surface area of the reactant, enables essentially 100% of the nickel reactant to come into contact with the fuel stream being desulfurized. The scrubber bed can also be formed from high surface area nickel coated alumina pellets, from a high surface area nickel coated ceramic extrusion, from high surface area nickel pellets, and from high surface area nickel extrudates.

TECHNICAL FIELD

The present invention relates to a method and structure fordesulfurizing gasoline, diesel fuel or like hydrocarbon fuel streams soas to render the fuel more suitable for use in a mobil vehicular fuelcell power plant assembly or in an internal combustion engine. Moreparticularly, the desulfurizing method and structure of this inventionare operable to reduce the amount of organic sulfur compounds found inthese fuels to levels which will not poison the catalysts in the fuelprocessing section of the fuel cell power plant assembly and will notharm components of an internal combustion engine. The method andstructure of this invention comprise a highly porous nickel coatedreactant bed which has an extended useful life cycle due to theinclusion of the porous nickel coat. The nickel in the coat is reducedfrom nickel oxide to nickel after being applied to the scrubber bedsupport. The reduced nickel removes sulfur from the fuel stream byconverting the sulfur to nickel sulfide that deposits on the reactantcoated surfaces of the scrubber bed.

BACKGROUND OF THE INVENTION

Gasoline, diesel fuel, and like hydrocarbon fuels have generally notbeen used as a process fuel source suitable for conversion to a hydrogenrich stream for small mobile fuel cell power plants due to the existenceof relatively high levels of naturally-occurring complex organic sulfurcompounds. The presence of sulfur results in a poisoning effect on allof the catalysts used in the hydrogen generation system in a fuel cellpower plant. Conventional fuel processing systems used with stationaryfuel cell power plants include a thermal steam reformer, such as thatdescribed in U.S. Pat. No. 5,516,344. In such a fuel processing system,sulfur is removed by conventional hydrodesulfurization techniques whichtypically rely on a certain level of recycle as a source of hydrogen forthe process. The recycle hydrogen combines with the organic sulfurcompounds to form hydrogen sulfide within a catalytic bed. The hydrogensulfide is then removed using a zinc oxide bed to form zinc sulfide. Thegeneral hydrodesulfurization process is disclosed in detail in U.S. Pat.No. 5,292,428. While this system is effective for use in largestationary applications, it does not readily lend itself to mobiletransportation applications because of system size, cost and complexity.Additionally, the fuel gas stream being treated must use largequantities of process recycle in order to provide hydrogen in the gasstream, as noted above.

Other fuel processing systems, such as conventional autothermalreformers, which use a higher operating temperature than conventionalthermal steam reformers, can produce a hydrogen-rich gas in the presenceof the aforesaid complex organic sulfur compounds without priordesulfurization. When using an autothermal reformer to process raw fuelswhich contain complex organic sulfur compounds, the result is a loss ofautothermal reformer catalyst effectiveness and the requirement ofreformer temperatures that are 200° F.-500° F. (93° C.-260° C.) higherthan are required with a fuel having less than 0.05 ppm sulfur.Additionally, a decrease in useful catalyst life of the remainder of thefuel processing system occurs with the higher sulfur content fuels. Theorganic sulfur compounds are converted to hydrogen sulfide as part ofthe reforming process. The hydrogen sulfide can then be removed using asolid absorbent scrubber, such as an iron or zinc oxide bed to form ironor zinc sulfide. The aforesaid solid scrubber systems are limited, dueto thermodynamic considerations, as to their ability to lower sulfurconcentrations to non-catalyst degrading levels in the fuel processingcomponents which are located downstream of the reformer, such as in theshift converter, or the like.

Alternatively, the hydrogen sulfide can be removed from the gas streamby passing the gas stream through a liquid scrubber, such as sodiumhydroxide, potassium hydroxide, or amines. Liquid scrubbers are largeand heavy, and are therefore useful principally only in stationary fuelcell power plants. From the aforesaid, it is apparent that currentmethods for dealing with the presence of complex organic sulfurcompounds in a raw fuel stream for use in a fuel cell power plantrequire increasing fuel processing system complexity, volume and weight,and are therefore not suitable for use in mobile transportation systems.

An article published in connection with the 21 st Annual Power SourcesConference proceedings of May 16-18, 1967, pages 21-26, entitled “SulfurRemoval for Hydrocarbon-Air Systems”, and authored by H. J. Setzer etal, relates to the use of fuel cell power plants for a wide variety ofmilitary applications. The article describes the use of high nickelcontent hydrogenation nickel reactant to remove sulfur from a militaryfuel called JP-4, which is a jet engine fuel, and is similar tokerosene, so as to render the fuel useful as a hydrogen source for afuel cell power plant. The systems described in the article operate atrelatively high temperatures in the range of 600° F. (320° C.) to 700°F. (380° C.). The article also indicates that the system tested wasunable to desulfurize the raw fuel alone, without the addition of largequantities of water or hydrogen, due to reactor carbon plugging. Thecarbon plugging occurred because the tendency for carbon formationgreatly increases in the temperature range between about 550° F. (290°C.) and about 750° F. (460° C.). A system operating in the 600° F. to700° F. range would be very susceptible to carbon plugging, as was foundto be the case in the system described in the article. The addition ofeither hydrogen or steam reduces the carbon formation tendency bysupporting the formation of gaseous carbon compounds thereby limitingcarbon deposits which cause the plugging problem.

It would be highly desirable from an environmental standpoint to be ableto power electrically driven vehicles, such as an automobile, forexample, by means of fuel cell-generated electricity; and to be able touse a fuel such as gasoline, diesel fuel, naphtha, lighter hydrocarbonfuels such as butane, propane, natural gas, or like fuel stocks, as thefuel consumed by the vehicular fuel cell power plant in the productionof electricity. In order to provide such a vehicular power source, theamount of sulfur in the processed fuel gas would have to be reduced toand maintained at less than about 0.05 parts per million.

The desulfurized processed fuel stream can be used to power a fuel cellpower plant in a mobile environment. The fuel being processed can begasoline or diesel fuel, or some other fuel which contains relativelyhigh levels of organic sulfur compounds such as thiophenes, mercaptans,sulfides, disulfides, and the like. The fuel stream is passed through anickel desulfurizer bed wherein essentially all of the sulfur in theorganic sulfur compounds reacts with the nickel reactant and isconverted to nickel sulfide leaving a desulfurized hydrocarbon fuelstream which continues through the remainder of the fuel processingsystem. U.S. Pat. No. 6,129,835, granted Oct. 10, 2000; and U.S. Pat.No. 6,156,084, granted Dec. 5, 2000 describe systems for use indesulfurizing a gasoline or diesel fuel stream for use in an internalcombustion engine; and a mobile fuel cell vehicular power plant,respectively. The desulfurization beds in the aforesaid systems, bothfixed and mobile, would typically utilize alumina pellets which havebeen admixed with the nickel reactant prior to being formed. Thus thealumina powder and nickel powder are mixed together and the pellets arethen formed from the mixture. Using this procedure, a major portion ofthe nickel reactant ends up in the interior of the pellets, and isunable to contact the fuel stream being desulfurized, and thus iswasted. The use of pelletized desulfurization beds using a nickelreactant is thus inefficient to a certain extent.

U.S. Pat. No. 6,140,266, granted Oct. 31, 2000 describes a compact andlight weight catalyst bed which is designed for use with a fuel cellpower plant which catalyst bed is useful in a fuel cell power plantreformer assembly. The content of this patent is incorporated into thisapplication in its entirety. The foam support provides a very highsurface area bed with excellent flow through characteristics. The use ofsuch an open cell foam support would provide a fuel desulfurizing bedthat would ensure that essentially 100% of the nickel reactant would beexposed to the fuel stream being desulfurized. Thus, the use of an opencell foam support member in a nickel-based reactant desulfurizing bedwould greatly increase the efficiency of the desulfurizer and alsoincrease its useful life.

We have discovered a way to further increase the useful life of a sulfurscrubber bed and sulfur scrubbing method, by further increasing thesurface area of the reactant, irrespective of the reactant supportstructures utilized in the scrubber bed. Our improvement involves theuse of a highly porous nickel oxide reactant coating which is applied toall exposed surfaces in the scrubber bed and thereafter reduced tonickel. The use of the highly porous nickel reactant coating increasesthe useful life of sulfur scrubber beds using alumina or silica pelletsas the reactant support, or using an open cell porous foam as thereactant support, or using a honeycomb-type monolith structure as thereactant support.

DISCLOSURE OF THE INVENTION

This invention relates to an improved desulfurizing bed structure andmethod for processing a gasoline, diesel, or other hydrocarbon fuelstream over an extended period of time, so as to remove substantiallyall of the sulfur present in the fuel stream, which structure and methodprovide a longer sulfur removal useful life. The bed structure andmethod of this invention include a support member onto which a highlyporous nickel oxide material is deposited. The nickel oxide coating ishighly porous, i.e., it has randomly distributed micro pores on itssurface and has a very high surface area. After the nickel oxide isreduced to nickel, the micro pores will vary in size from one micron tofifty microns in diameter. With the support micro porosity, the reducednickel reactant coat will result in a nickel surface area of over fiftysquare meters per gram (M²/gm) of reactant in the scrubber bedstructure. This micro porosity and increase surface area greatlyincrease the amount of nickel in the scrubber bed which is available andable to react with sulfur in the fuel stream so as to remove the sulfurfrom the fuel stream and convert it to nickel sulfide on the scrubberbed surface. When all of the available nickel sites on the scrubber bedsurface have been converted to nickel sulfide, then the scrubber bedwill be deemed to have reached a “sulfur breakthrough” condition andwill be unable to convert further sulfur in the fuel stream to producethe desired low sulfur content fuel. By using the highly porous nickelcoating in lieu of a standard nickel coating, the useful life of thescrubber bed is extended by a factor of about five.

Gasoline is a hydrocarbon mixture of paraffins, naphthenes, olefins andaromatics, whose olefinic content is between 1% and 15%, and aromaticsbetween 20% and 40%, with total sulfur in the range of about 20 ppm toabout 1,000 ppm. The national average for gasoline in the United Statesis 350 ppm sulfur. The legally mandated average for the State ofCalifornia for gasoline is 30 ppm sulfur. As noted above, the sulfurcontent of gasoline must be less than about 0.05 ppm to be useful in afuel cell power plant as a source of hydrogen. This low level is alsobeneficial in that it minimizes internal combustion engine damage fromsulfur.

The effectiveness of a nickel adsorbent reactant to adsorb organicsulfur compounds from gasoline depends on the relative coverage of theactive reactant sites by adsorption of all the various constituents ofgasoline. In other words, the desulfurization process depends on theamount of competitive adsorption of the various constituents ofgasoline. From the adsorption theory, it is known that the relativeamount of adsorbate on an adsorbent surface depends primarily on theadsorption strength produced by attractive forces between the adsorbateand adsorbent molecules and secondarily on the concentration of theadsorbate in the gasoline, and temperature. Coverage of a reactantsurface by an adsorbate increases with increasing attractive forces;higher fuel concentration; and lower temperatures. Relative to gasoline,Somorjai (Introduction to Surface Chemistry and Catalysis, pp, 60-74)provides some relevant information on the adsorption of hydrocarbons ontransition metal surfaces, such as nickel. Saturated hydrocarbons onlyphysically adsorb onto the nickel reactant surface at temperatures whichare less than 100° F. (40° C.), therefore paraffins, and most likelynaphthenes, won't compete with sulfur compounds for adsorption sites onthe nickel reactant at temperatures above 250° F. (121° C.) and 300° F.(149° C.).

On the other hand, unsaturated hydrocarbons, such as aromatics andolefins, adsorb largely irreversibly on transition metal surfaces evenat room temperature. When an unsaturated hydrocarbon such as an aromaticor an olefin adsorbs on a transition metal surface, and the surface isheated, the adsorbed molecule rather than desorbing intact, decomposesto evolve hydrogen, leaving the surface covered by the partiallydehydrogenated fragment, i.e., tar or coke precursors. At 350° F. (177°C.), unsaturated hydrocarbons are nearly completely dehydrogenated, andthe dehydrogenated tar fragments form multiple carbon atom-to-nickelreactant surface bonds. This explains why aromatics and olefins ingasoline, in the absence of oxygenated compounds in appropriateconcentrations, will deactivate the nickel reactant from adsorbingsulfur after a relatively short period of time. To prevent this fromoccurring, it is preferred to use gasoline which contains an oxygenate,such as ethanol, methanol, MTBE, or the like, in order to generate asmall amount of hydrogen to prevent dehydrogenation of aromatics andolefins in the gasoline.

Further nonessential but enabling information relating to this inventionwill become readily apparent to one skilled in the art from thefollowing detailed description of a preferred embodiment of theinvention when taken in conjunction with the accompanying drawings inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will becomereadily apparent to one skilled in the art from the following detaileddescription of a preferred embodiment of the invention when taken inconjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of one form of an open cell foam monolithsulfur scrubber bed formed in accordance with this invention;

FIG. 2 is a fragmented perspective view of a heat transfer component andfoam sulfur scrubber bed assembly which are bonded together;

FIG. 3 is a perspective view of a sheet metal monolith sulfur scrubberbed formed in accordance with this invention;

FIG. 4 is an end elevational view of the scrubber bed of FIG. 3;

FIG. 5 is a fragmented perspective view of an extruded ceramic monolithsulfur scrubber bed formed in accordance with this invention; and

FIG. 6 is a graph comparing the performance of sulfur scrubber bedsformed in accordance with this invention with conventional sulfurscrubber beds formed in accordance with the prior art.

SPECIFIC MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, there is shown in FIG. 1 a perspectiveview of a rectilinear form of a sulfur scrubber bed formed in accordancewith this invention, which bed is denoted generally by the numeral 2.The scrubber bed 2 is a monolithic open cell foam support componentwhich includes a lattice network of tendrils 4 that form a network ofopen cells 6 which are interconnected in the X, Y and Z directionswithin the bed 2. The interconnected open cells 6 are operable to forman enhanced fuel gas mixing and distribution flow path from end 8 to end10 of the bed 2. The open cells 6 and the tendrils 4 also provide a verylarge nickel reactant-available surface area for coating in the bed 2.The core or support member of the foam scrubber bed 2 can be formed fromaluminum, stainless steel, an aluminum-steel alloy, silicon carbide,nickel alloys, carbon, graphite, a ceramic, or the like material. Onepreferred material is cordierite, which is a porous ceramicalumina/silica mineral.

Typically, the bed 2 is coated with the highly porous nickel oxidesurface layer in the following manner. A coat of the highly porousnickel oxide and an acid, such as acetic acid, nitric acid, or the like,is applied to all outer and interstitial surfaces in the foam core 2.The washcoat can be applied to the core 2 by dipping the core 2 into awashcoat solution, or by spraying the washcoat solution onto the core 2.The washcoated core 2 is then calcined so as to form the solidifiedhighly porous nickel oxide layer on all surfaces of the core 2. Thehighly porous nickel oxide wash coat is preferably one produced bySud-Chemie, Inc. by co-precipitating a highly dispersed nickel withnon-reducible oxides, such as alumina, silica, rare earth oxides, or thelike. The inclusion of the non-reducible oxides provides the enhancedsurface area for the nickel reactant, and prevents sintering of thenickel surface, which would reduce the surface area thereof. Theco-precipitation of nickel and the oxides forms the washcoat, and thenthe washcoat is applied to the support.

FIG. 2 is a fragmented perspective view showing separate members of thenickel reactant coated foam components 2 which are bonded to heattransfer components 48. By bonding the open cell foam components 2 to anadjacent heat transfer components 48, which can be planar walls, orcoolant conduits, continuation of the high thermal conductivity of thefoam 2 into the heat transfer component 48 is achieved. The heattransfer components 48 can made of aluminum, stainless steel,steel-based alloys containing aluminum, or high nickel alloys, asdictated by requirements of the system into which the components 2, 48are incorporated.

Referring now to FIG. 3, there is shown a monolithic form of a sulfurscrubber bed which is denoted generally by the numeral 12. The scrubberbed 12 is formed from sheet metal components that can be coated with thehighly porous reducible nickel oxide layer described herein. The bed 12can be formed from a series of planar components 14 which are spacedapart and are separated by honey comb components 16 which are alsoformed from a washcoatable sheet metal. The components 16 and the planarcomponents 14 combine to form through passages 18 which have theirsurfaces coated as indicated by the numeral 20 in FIG. 4. The fuelstream being desulfurized flows through the passages 18 in the directionindicated by the arrows A.

Referring now to FIG. 5, there is shown yet another embodiment of asulfur scrubber module which is formed in accordance with thisinvention. The desulfurizer module shown is formed from an extrudedceramic monolith which is denoted generally by the numeral 22. Themonolith is preferably formed from cordierite, which is analumina-silica mineral which can be artificially manufactured. Themonolith 22 includes a plurality of crisscrossing webs 24 which formthrough passages 26 that extend through the monolith 22. All of theexposed surfaces on the monolith 22 are coated with the reducible porousnickel oxide material. The fuel being desulfurized passes through themonolith 22 in the direction of the arrows B. The sulfur scrubber can beformed for a single monolith 22 or by a bundled plurality of themonoliths 22.

In addition to the above-identified monolith reactant support members,we have also discovered that the porous reducible nickel oxide materialdescribed herein will increase the useful life of a sulfur scrubberstation which uses packed pellets as the reactant support. The pelletswill typically be formed from alumina powder which is compressed intopellet form. The surface of the formed pellets is then coated with thereducible nickel oxide material which is then reduced to form the highlyporous nickel reactant. This method of coating the support pelletsgreatly enhances the surface area of the reactant on the pellets anddoes not result in unusable reactant, which can result when the pelletsare formed from a mixture of alumina powder and nickel powder, whereinsome of the nickel will be encapsulated inside of the pellets and thusbe rendered unusable in the desulfurizing reaction.

Referring now to FIG. 6, there is shown a graph which illustrates theimproved performance of nickel based sulfur scrubber beds that areformed in accordance with this invention as compared with nickel basedsulfur scrubber beds formed in accordance with the prior art. The priorart scrubber beds used in the comparison shown in FIG. 6 were formedfrom alumina pellets that incorporated nickel powder as the sulfuradsorbent.

The Y axis of the graph indicates the concentration of sulfur in thefuel stream being processed as measured by a sulfur sensor incorporatedinto the scrubber bed. The X axis of the graph shows the hours ofservice for the scrubber bed.

The scrubber beds formed in accordance with this invention were madefrom alumina pellets that were coated with two different but relatedcoats of the enhanced surface area nickel oxide that were both reducedto a nickel reactant. The graph illustrates a sulfur breakthrough levelof 0.05 ppm sulfur, shown as line 28. This breakthrough level is theconcentration of sulfur in the fuel stream which is the uppermost sulfurconcentration that a fuel cell fuel processing assembly can tolerate.When the sulfur scrubber bed becomes incapable of producing a fuel gasstream having less than 0.05 ppm sulfur in it, the scrubber bed will beconsidered to be inoperable or spent.

As noted above, the scrubber beds that were formed in accordance withthe prior art used a lower surface area, i.e., less than fifty M²/gmsurface area, nickel sulfur adsorbent incorporated into alumina pellets.The plots of sulfur concentration v. time for the prior art sulfurscrubber beds are indicated by the lines 30 and 32. It will be notedthat sulfur breakthrough occurred at approximately five hundred hours ofbed operation; and at approximately seven hundred hours as indicated bythe plots 30 and 32 of the two prior art sulfur scrubber beds tested.

The performance plots of the two versions of sulfur scrubber beds thatwere formed in accordance with this invention are denoted by the lines34 and 36. It will be noted that sulfur breakthrough occurred atapproximately twenty four hundred hours and approximately three thousandhours as indicated by the plots 34 and 36 of the two sulfur scrubberbeds tested that were formed in accordance with this invention.

It will be noted that the sulfur scrubber beds formed in accordance withthe invention that are depicted in FIG. 6 were formed with pelletizedsupport members for the nickel reactant, and still produced markedimprovement in performance as compared to the prior art which alsoutilized pelletized support members for the nickel reactant.

When sulfur scrubber bed supports are formed from the foams and extrudedmonoliths described above, and are used to support the high surface areanickel reactant, the improvements in hours of service will be evengreater than shown in FIG. 6, because the surface area of the foam andmonolith supports which is washcoated with the reduced nickel reactantis volumetrically much greater than the surface area of a volume ofpacked alumina pellets which are washcoated with the nickel reactant.

Monolith open cell foam cores of the type described above can beobtained from ERG Energy Research and Generation, Inc. of Oakland,Calif. which cores are sold under the registered trademark “DUOCEL”.Another source of the foam cores is Porvair, Inc., of Ashville, N.C.

A high surface area reducible nickel oxide coat material of the typedescribed herein above can be obtained from Sud-Chemie, Inc. ofLouisville, Ky. The nickel oxide material available from Sud-Chemie isidentified by Sud-Chemie's product designations T-2496 and T-2694A. Thenickel oxide coat material is the most preferred form of the nickelreactant due to longer term stability. Alternatively, the nickel oxidematerial could be extruded to form a high surface area support per sewithout requiring a separate nickel oxide coating. Thus, the nickeloxide material could be used as a coating on a support material, or itcan be used as a reactant without a separate support material. Thenickel oxide is reduced to nickel prior to use.

Since many changes and variations of the disclosed embodiments of theinvention may be made without departing from the inventive concept, itis not intended to limit the invention other than as required by theappended claims.

1. (canceled)
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 5. (canceled) 6.(canceled)
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 8. (canceled)
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 10. (canceled) 11.A method for producing a sulfur scrubbing assembly that is operative toremove sulfur from a gasoline or diesel fuel stream, said methodcomprising the steps of: a) providing a support structure for theassembly; b) providing said support structure with a coating thatincludes nickel oxide and that has a surface area of greater than aboutfifty square meters per gram of said coating; and c) reducing saidnickel oxide in said coating to nickel.
 12. The method of claim 11wherein said support structure is porous.
 13. The method of claim 12wherein said porous support structure is a foam.
 14. The method of claim12 wherein said porous support structure is an extruded ceramicmonolith.
 15. The method of claim 11 wherein said coating is aco-precipitated mixture of nickel and one or more high surface areanon-reducible oxide.
 16. (canceled)